This application is copending with application Ser. No. 039,341, filed 4-7-87, now abandoned. The invention relates to a process for the preparation of D-(+)-biotin from L-cysteine or L-cystine or L-serine via an optically active (7R)-1H,3H-imidazol[1,5-c]azole as an intermediate product.
The invention was based on the object of providing a new process for the preparation of optically active D-(+)-biotin which avoids the procedure of racemate resolution and hence the discarding or recycling of the undesired enantiomer.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
Processes for the stereospecific synthesis of D-(+)-biotin from sugars of suitable configuration are known. Thus, D-mannose is used as the starting material in Tetrahedron Letters No. 32, pages 2765-2766 (1975), D-glucose is used as the starting material in Agric. Biol. Chem. No. 42, Page 465 (1978), and D-arabinose is used as the chiral starting material in German Offenlegungsschrift 3,122,562 and German Offenlegungsschrift 3,320,140.
All these processes are characterized, however, by a high number of synthesis steps with consequently a low overall yield. The intermediate stages, which usually cannot be crystallized because of their sugar nature, are frequently obtained only in unsatisfactory purity, and because of their polyfunctionality and the associated chemical instability, require observance of comparatively narrow reaction parameters. A number of sugars are also inaccessible from natural sources, which results in a high price.
The use of L-cysteine, such as is known from U.S. Pat. No. 4,009,172, U.S. Pat. No. 4,130,713, U.S. Pat. No. 4,337,345 and Journal of the American Chemical Society No. 99, page 7020 (1977), indeed avoids handling of unstable intermediate stages, but in contrast leads to only an unsatisfactory yield of optically active D-(+)-biotin by a total of 18 reaction stages with removal of undesired isomers.
In another process, substituted 3H,5H-imidazol[1,5-c]-tetrahydrothiazoles from which optically active biotin is obtained after racemate resolution are described in Journal of the American Chemical Society No. 105, Page 5946 (1983) and in European Published Application No. 0,094,776.
Since the comparatively high number of stages associated with in some cases moderate yields and the need for optical resolution also makes these starting substances to be poorly suitable for the preparation of D-(+)-biotin, there continued to be a need for a suitable process for simple economic stereospecific preparation of D-(+)-biotin.